1. Field of the Invention
The subject invention is directed generally to a shutdown system for controlling the fluid flow from a fuel metering unit to an engine, and more particularly, to a shutdown system associated with an aircraft engine that can quickly provide either a minimum flow of fuel to the engine or a complete shutdown of fuel delivery in response to an overspeed condition.
2. Background of the Related Art
Modern aircraft engines function under operating conditions that often include harsh extremes of weather and performance demands. Under such circumstances, engine malfunction can occur. For example, an engine may increase in speed in an uncontrolled manner, i.e. an overspeed condition. If unremedied, an overspeed condition can cause an engine to fail resulting in loss of control and catastrophe for the aircraft. As a result, designers have incorporated shutdown systems in the fuel pump control system to stop fuel delivery to the engine and, in turn, shut down the engine to maintain safety and control. Typically, a shutdown system employs a fast acting solenoid or other well-known means. For examples, see U.S. Pat. Nos. 6,508,225; 5,435,718; and 5,357,935, which are incorporated herein by reference in their entirety.
In certain conditions a complete shutdown of the engine may not be the best possible solution. Stopping the undesirable behavior of the engine while maintaining the engine in an operational state would allow the pilot an opportunity to have improved control of the aircraft. If the improved control is not achieved, the complete shutdown of the malfunctioning engine could then be implemented. In view of the above, it would be desirable to provide a shutdown system for a fuel metering unit which has two available modes of shutdown, one mode would be a minimum fuel flow condition to maintain the engine in an operational state and another mode would be a zero fuel flow condition for a total engine shutdown.